The present invention relates to valves in general and, more in particular, to an improved valve seat and seal of a valve.
Flow control valves in their off position must prevent leakage through the valve. Closure is effected at a seat against which a valving element bears. Typically either the valve element or the seat, or both, has a seal of soft material. The soft material conforms to irregularities in the sealing zone to prevent leakage. For example, a score in a seat of hard material would be closed by a soft seal.
Soft seal materials often are not suitable to handle certain types of fluids. Natural gas, for example, will in time attack, degrade and fail rubber O-rings. A typical failure is manifested by a swelling of the seal. With swelling, the seal can blow out of its seat or become sheared by moving valve parts.
At this time, Teflon is the only known material that will not react with such fluids as natural gas. Teflon is a trademark of E. I. DuPont and Company for a polytetrafluoroethylene.
Teflon presents its own problems and one of them is that it is not elastic. Another problem with Teflon is that it has very poor cold flow characteristics.
When soft seals are employed on a valve and throttling is required it is not uncommon, especially when a pressure drop because of throttling is considerable, to erode soft seal material by rapidly flowing fluid. Obviously such erosion can result in seal failure.